Apparatus for effecting dissolution or lixiviation



June 2, 193s. w. H, ALLEN ET AL 2,042,818

APPARATUS FOR EFFECTING'-DISSOLUTION OR LIXIVIATION 3 Sheets-Sheet lFiled Oct. 28, 1933 `une 2, 1936; w. H. ALLEN ET Al.

APPARATUS FOR EFFECTING DISSOLUTION OR LIXIVIATION Filed Oct. 28, 1933 3Sheets-Sheet 2 311m@ 2, 1935 w. H. ALLEN Er AL 2,042,818

APPARATUS FOR EFFECTING DISSOLUTION OR LIXIVIATION Fled Oct. 28, 1953 5Sheets-Sheet 5 .5" uids are immiscible.

Patented .lune 2, i936 TATES FATENT OFFICE APPARATUS FOR EFFE C'NGDISSOLUTION OR LIXIVIATHON Application October 28, 1933, Serial No.695,644

8 Claims.

This invention relates to an apparatus for effecting the dissolution orlixiviation of solids, and immiscible liquids, and has particularreference to an apparatus for producing solu- '5 tions of solutes at adenite temperature and having denite concentration of such solutes.

The apparatus of the present invention is of particular Value in rapidlyproducing saturated solutions of a solute, free from -any excess orundissolved particles: of solute. Heretofore, when it Was desired toproduce a concentrated solution of a solid, or of a liquid in anotherliquid in which it is immiscible, particularly a saturated solution freefrom any particles of undissolved --15 matter, it has been generallynecessary to effect the solution in a batch process, in Which thesolvent is brought to equilibrium with the solute by agitation, afterwhich the contents are permitted to' settle before a clear solution canbe Withdrawn. '2.0 In prior practice, it has been necessary, if it wasdesired to produce a saturated solution of a solid in a continuousmanner, to use two connected pieces of apparatus, in the rst of whichthe solvent and solute are agitated together continuous- 25 ly toproduce a. saturated solution. From such apparatus it has been necessaryto withdraw a sludge of the saturated solution and undissolved solute toa second apparatus, such as a thickener, to separate the solution fromthe excess solute, 30 which, latter is then returned to the mixing anddissolving apparatus.

It is the primary object of the present invention to provide anapparatus for producing solutions of solutes and especially solids bywhich a concentrated or saturated solution may be rapidly obtained andfrom which a clear solution may be withdrawn free from any of the soluteWhile the mixing operations are still beingperformed in the apparatus.40 It is a further object of the present invention to provide anapparatus in which a saturated solution of a solute may be continuouslyproduced and withdrawn from the apparatus free fromany undissolvedmaterial.

The apparatus of the present invention has been particularly designedfor forming saturated solutions of a salt, but it may also be used inthe manipulation of sludges or mixtures of solutions and solids forother purposes. For example, the apparatus may be employed in thepreparation of concentrated solutions of solids by lixiviation orleaching of salts, ores, or the like. Also, the apparatus may beutilized for the preparation of solutions of liquids in solvents inwhich the liq- Herein, the description is given principally by referenceto the preparation of solutions of solids.

In the manufacture of many crystalline salts, it is often Idesired torefine crude salts byrecrystallization. This requires dissolution of thecrude 5 salt. In many instances, it is also desired to produce asolution having a definite concentration of the constituent. Forexample, in the production of borax from Searles Lake brine, crude saltscontaining minor impurities are crystallized from 10 a concentratedsolution also containing other salts. These crude salts are rened bydissolving them to form a solution of borax and recrystallizing the pureborax from this solution. In the recrystallization of the borax it isdesired to produce single nucleus crystals of good size. Thecryst-allization of borax to produce single nucleus crystals of goodsize is dependent, among other things, upon controlling the number ofcrystal seeds present. The control of the number of crystal nucleipresent ispreferably accomplished by starting with a solution free ofsolid particles of borax. The apparatus of the present invention enablesthe production of a concentrated solution of crude salts containing nosolid particles, which solution may be utilized for recrystallization ofthe salt in the desired form of crystals.

In the handling of many solids, it is desired to produce a solution of adefinite concentration, 3o which, however, is not saturated at the finaltemperature at which it is to be used. Such a solution may be preparedin the apparatus of the present invention by first carrying out thedissolution of the solid at a temperature at which the saturation valueof the salt in the solvent is equal to the desired concentration. Thissaturated solution is then rendered unsaturated by changing itstemperature to the desired extent. When the solute possesses asolubility which varies directly with the temperature, the desiredunsaturated condition is accomplished by heating. When the solubility is4an invert one, cooling of the saturated solution is utilized to obtainan unsaturated solution. Consequently, an unsaturated solution may beeasily prepared in accordance with the features of our invention, bothwhen the solubility curve increases with increasing temperature and whenit decreases therewith.

As applied to the refining of borax, for example, it has been founddesirable to eliect recrystallization of the borax from a solutioncontaining approximately 16% NazBiOv at a temperature of about 180 F. Inpreparing such a solution, the crude borax is dissolved in the apparatusof the present invention at a temperature of about F. to 145 F. At thistemperature the saturation concentration is approximately 16% NazBiO'i.'I'he saturated solution may then be heated to F. to provide a clear,solids-free solution, containing the desired amount of borax at thedesired temperature.

The preparation of controlled concentration Vsolutions in accordancewithout invention involves a regulation of the temperature of the solutionduring the digestion operation. When the substance being disolvedpossesses a low rate of solution, a large heat of solution (i. e.negative heat of crystallization), or both of these properties, we havefound that careful regulation of the temperature during digestion isoften difcult to accomplish. If the solute requires heat for solution,i. e. possesses a negative heat of solution, heat must be supplied insuicient quantity to 4both elevate the temperature of the solution tothe desired point and to compensate for the heat taken up during thedissolution process. Suitable cooling means are employed when heat isgiven 01T during the dissolving process, and in some cases the heatrequired for elevation of the temperature of the solution may besupplied by the heat given off during the solution process. We providemeans for conveniently accomplishing a careful regulation of thetemperature of the saturated solution. We thereby obtain solutionshaving accurately controlled concentrations.

The apparatus of the present invention is designed to prepare asaturated solution of a solid, which may be continuously withdrawn in aclear state by the provision of a chamber, in one portion of which thesolvent and solute undergo agitation together in order to effect rapidsolution, while in another portion of the chamber, partially separatedtherefrom by a suitable di- -vision wall or walls, the same body ofsolutions which has reached substantially the saturation value maybecome quiescent to permit the continuous withdrawal o-f a clearsaturated solution without the necessity of withdrawing any of the freeor undissolved solute. Temperature control in the dissolver tank orcontainer is accomplished by subjecting the mixture of solution andexcess solute to a primary heat treatment pre- Vious to its introductioninto the dissolver and to a secondary heating under careful control inthe dissolver. In particular, we found that ease of regulation of thesolution temperature is enhanced when the secondary heating isaccomplished through the use of steam injected into the solution duringthe dissolving process. 'Iime lag of control is thereby reduced andbalancing of rapid temperature fluctuations is improved.

The present invention, together with various further objects andadvantages thereof, will best be understood from reference to aparticular form or example of an apparatus embodying the invention. Forthis purpose, We have hereinafter described a preferred form or exampleof the apparatus. y q In the drawings:

Figure 1 represents a vertical section.

Figure 2 is a section along the line 2 2 of Figure 1.

Figure 3 is a sectional elevation of the impeller employed.

Figure 4 is a plan view of the impeller.

Figure 5 is a vertical sectional view of another form of settler.

Referring to Figures 1 and 2 ofthe drawings, the apparatus comprises anouter shell I, preferably of a cylindrical cross-section, having top andbottom closures 2 and 3 which together provide a chamber in which thedesired solutions are to b-e produced. I'he bottom closure 3 ispreferably dish-shaped and provided near its center with inlet pipe 3a,through which a mixture of solution and undissolved solute may beintroduced into the apparatus. Within the ap-` paratus there is providedsuitable means for effecting continued agitation, preferably by internalcirculation of the sludge in order to effect the desired solution of thesolute. Said agitating means preferably include a centrifugal impeller 4and a vertical circulating well. The circulating well is preferablyformed by a cylindrical shell 5 fixed concentrically within the outershell I by suitable means, such as rectifying vanes 6. The rectifyingvanes 6 are disposed in the annular space between the inner and outershells,

preferably four of the vanes being utilized. The

vanes are in the form of vertically positioned plates so as to serve thedual purpose of holding the inner shell 5 in position and of reducingswirling or vortex action of the solution during circulation.

The impeller 4 is preferably fixed to a drive-1 shaft 1 journalled inbearings 8 and 9 and sup-y ported by the top and bottom plates 2 and 3.

The production of saturated solutions in rapid manner is facilitated bythe provision of means for securing a positive circulation of the soluteand solution in such a manner as to maintain the undissolved solutecontinuously in suspension in the solution during the dissolving action.In order to best attain this end, the diameter of the inner shell 5 ispreferably made such that the cross-sectional area of the well will beabout onehalf the total cross-sectional area of the outer shell I. Thus,there is no difference in the velocity of the liquor throughout thecirculating path formed by the inner shell 5. In this manner, theapparatus avoids the formation of quiescent areas of liquid in whichsettling of the solids might occur. The relative areas or diameters ofthe inner and outer shells, however, may be varied without in some casesgreatly affecting the e'iciency of the apparatus. The inner shell 5 ismade to terminate sufficiently above the bottom plate 3 of the apparatusso as to provide a space for passage of fluid from the well into theannular space between vthe shells.. The vertical cross-sectional area ofthis space is preferably substantially equal to the area of the centerwell provided by the inner shell 5. The cross-sectional area of thecirculating path is thereby maintained substantially constantthroughout.

The impeller 4 is preferably disposed in this space provided below theinner shell. In its preferred form the impeller is a large volume, slowspeed unit capable of imparting substantially stream-line movement tothe solution. By "stream-line movement is meant circulation in whicheach unit volume of solution or sludge maintains a more or less constantrelation in position to every other unit volume of solution or sludge.Thus, swirling is not stream-line movement and is preferably a minimumin the circulation provided. Swirling and vortex action tendtoappreciably dissipate the forcel imparted by the impeller. The.impeller 4 is also preferably designed to discharge the liquorsubstantially entirely in a radial direction. The design ill() iofstheiimpellerfor-accomplishing .theseAA purposes Y.isrbestlillustrated inxFigures Band 4.

'The impeller comprises impelling vanes I0 mounted vertically upon abase plate II at an angleof approximately 45 with diameters pass- Lingthrough the inner edges of the vanes. The vaneslll are illustrated asshort straight pieces, but they may be of convolute contour. .Theconvolute contour, however, is practically straight Vnear the peripheryof ythe impeller, and since 'theiimpeller vanes Ill are utilized. onlyat near the periphery of the impeller, the straight and .convolutecontours are substantially equivalent.

:The'base plate II is an annular plate tapered .upwardly where it meetsthe vanes IB at an angle corresponding to the taper on the bottom plate3 of the apparatus. For supporting the base ,plate I`I Aand impellervanes Il) on the shaft '1, thereis provided a spider I2, having upwardlyand -inwardly extending braces I3, connecting at one `end. with the baseplate II and at their other end with a hub It for the impeller which iskeyed to the shaft In order to prevent `undue liquor slippage throughthe impeller, an :annular cover plate I5 is mounted on the tops .o'ffthevanes I0. This top plate is preferably formed at a taper parallel tothat of the bottom plate II.

'The diameter of the impeller is preferably equivalent to that of thewell 5 in order to facilitate the maintenance of stream-line movementthroughout the system. For vthe same reason, the height of the vanes Illis such that the area 'defined by the outer edges of the plates II andI5 is equivalent to the cross-sectional area of .the center wellprovided by the inner shell 5. In this way, the cross-sectional area ofthe circulating path through the impeller and around the well may bemade substantially constant.

'I'he mixture of solution and undissolved solute introduced through theinlet 3a circulates directly through the impeller and into thecirculating body of the solution. Thorough mixing of the freshingredients with the solution and solute in-the dissolver is therebyaccomplished. Also, byzspaoing Ythe annulus II only a short distance.from the bottom 3, a stream of solution is co-nytinuously by-passedfrom the main circulation stream at the edge of the impeller into thespace beneath the impeller and back into the main stream. The likelihoodof deposition of undissolved solute in the dead space below theirnpeller is thereby decreased.

The rate of upward iiow created by the impeller shouldpreferably besufficient to prevent vv.packing'o'f settled particles in any part ofthe system and to maintain all particles in suspenfsion in the solution.In some cases it may be :desirable to employ a rate of flowsubstantially lequal Yto or even greater than the settling rate `of thelargest particles in suspension in the solution. We have found thatunder certain coniditions and particularly when dense sludges are.present a rate less than the settling rate of the largest suspendedparticles can be employed.

'The apparatus is also provided with means for baffling oi a portion ofthe mixture of solution and suspended solute from the main body thereofvundergoing agitation or circulation. This baflling .means permitssolution which has reached the .desired concentration to becomequiescent so that suspended undissolved solute may settle therefrom.This may be accomplished by the provi- .sionof acone I6 disposed abovethe inner shell The diameter o-f the within theouter shell flows overthe upper edge 110 of the cone. It is supported concentrically withinthe inner shell I by suitable means, such as the .straps Il. `At itslower end it is preferably braced from the inner shell 5 by braces I8.The main body of the settler or baffle cone I6 preferably has'a slopesomewhat greater than the angle of repose of the settled particles. Atthe bottom the cone is provided with an outlet connecting Vwith theshort nipple I9, which nipple I9 is vof greater diameter than that ofthe shaft l. 'Ihe shaft 'I is preferably provided with a helical screwsection 2S where the shaft extends through the nipple i8. The mechanismfor operating the shaft I with the screw section 2B and the impeller-imay be any suitable drive means, not shown, preferably connected to theupper end of the shaft. The rotating helical screwsection 2G ispreferably of large pitch and. of a diameter suiiicient to provide aclose t in the nipple I9.

It serves to forcibly eject any solids which may settle in the conicalsettler I6 into the circulating zone existing therebelow.

The apparatus also preferably comprises suitable means, such as theoutlet pipe 2|, for withdrawing the liquor from a point near the axis ofthe apparatus, and preferably slightly above Vthe cone I6. This isdirectly opposed to the conventional settler operation in which themixture of solids and liquids is introduced near the middle at the topand the clarified solution withdrawn as an overflow at the periphery.Two zones of localized disturbance exist in a settler, one at the inletarea and the other at the outlet area. In the conventional settler, thelocation of the inlet at an axial point at the top creates an area ofgreat localized disturbance and turbulence in the center of the settler.Settling is therefore diminished until the liquor iiows beyond this areaof localized disturbance. In the apparatus of the present invention theintensity of the disturbance caused by the introduction of the liquor orsuspension of solids in liquor into the settling cone is greatlyminimized by distributing the incoming liquor' around the periphery ,ofthe settler. Settling then occurs 'quickly and the settled solids sooncome in contact with the walls of the settler and pass down to theoutlet orifice I9. By so introducing the suspension of undissolvedsolids at the periphery of the settler and locating the outlet conduitnear the middle and the top thereof, we are enabled to continuously drawoff saturated solution which is substantially free of suspended solute.

In the operation of the apparatus, the solution and excess undissolvedsolute are continuously introduced through the inlet 3e. The impeller 4is continuously operated to effect circulation of the solids andsolution around the inner shell 5, and the clear saturated solution iscontinuously I Withdrawn through the outlet 2|. In operation, theapparatus may, if desired, be operated entirely full of liquid. Thecirculation of solute and solution over the top of the internal shell 5vheating within the dissolver.

draws most of the suspended solids down'through the shell, and only asmall portion of undissolved solute overflows the edges of the bailleand settling cone I5. This small portion will settle out of the liquorwithin the settling cone I6, if the dimensions of the unit are correctfor the particular materials treated.

The rate of Vremoval of the solution and its temperature are socontrolled that the liquor is retained in contact with suspendedsolute'until saturation or substantial saturation of the solution withrespect to the solute is reached. 'Ihe control of the temperature of thesolution being prepared involves two major factors. Suflicient heat mustbe supplied or withdrawn to counterbalance the heat of solution ofthesolute in the solvent and to raise or lower the temperature to thedesired point for producing the saturated solution. When the solubilityincreases directly with temperature, heat will be taken up duringsolution and also a high temperature must be used for the production ofa concentrated solution. Thus for this class of salts, considerable heatwill be required during the process. If the solute possesses an invertsolubility curve, heat will be given off during the solution process andmore concentrated solutions will exist at the lower temperature.Consequently cooling or refrigeration will be required for thedissolution of such solutes.

A careful control of the temperature in thedissolver is often diiiicultto accomplish. This is particularly true when the solute is slow todissolve and when a large heat of solution. is involved. Borax, forexample, possesses a comparatively slow rate of solution and a heat ofsolution of approximately 26,000 calories per gram-mol. We have foundthat the heat required for maintenance of a uniform temperature withinthe dissolver will Vary considerably.

In accordance with another feature of Athis invention, we accomplish theheating in two steps. We have found that a close. control of the finaltemperature is facilitated by effecting a portion of the total heatingrequired in a primary operation and the remainder in a secondary Thedistribution of the heating between the primary and secondary treatmentswill Vary with various materials being dissolved. The heating requiredin the dissolver is desirably accomplished by injectingA stream underclose control. We have found that close control is particularly wellaccomplished when this secondary heating is by means of steam injectedunder control into the solution in the dissolver. We supply steamnozzles or injectors 22 which inject steam preferably into the path ofliquid in the annular space between the twoshells and 5 of theapparatus. The mechanism for controlling the amount of steam introducedmay be any suitable accurate thermostatic control device operatingagainst the solution in the dissolver or in the outlet conduit.

The heating accomplished by steam may if desired be provided by the useof an external lheater in parallel with the dissolver. A portion of thesolution is then continuously withdrawn,

-passed through the heater and returned to the dissolver. When using anexternal heater in parallel with the dissolver for temperature controlpurposes, the circulation effected through the withdrawal of solutionand solute and its return may conveniently replace the combination of'internal well and centrifugal impeller described'herein. Thatis, anoutside pump transferring solution and solute from the dissolver throughthe heater and returning it to the dissolver can be used to serve as acirculating means.

Thermostatic control of the heating to be employed or effected in anexternal heater is also desirable, but close control is often moredithcult to effect than with heating by steam injection.

The production of aclear liquor is dependent upon the settling areaprovided in the settler i8 and to some extent upon the presence of azone of quiescence in the tank and just below the rim of the settler.The amount of settling which will result in any given settling zoneisdependent among other factors, upon the degree of quiescence orconversely upon the presence or absence of influences which 'tend tocause turbulence or liquor disturbance in the settling area. In thepresent instance, the settler is preferably located sufficiently abovethe circulation well that the greater part of the velocity head presentin the circulation path is dissipated before the solution reaches theinlet rim of the settler. The actual settling area formed by the settlerper se is then located in an area removed from the disturbing influenceof the circulation effected in the lower part of the dissolver. Someadditional settling may be accomplished by increasing the distance bentween the settler rim and the top of the circulation well to therebyincrease the extent of the quiescent area.

The creation of this quiescent area between the circulation well and therim of the settler may be enhanced by the use of suitable baiile plates30 preferably stream-lined to possess a concave surface on their lowerfaces and attached to the inner surface of the dissolver'shell l. Thesebaffles will be preferably so disposed as to divert the upward directionof flow of the vliquor in the circulation path toward the interior ofthe circulation well. The velocity head of the liquor moving toward therim of the settler is then appreciably reduced and the production of thedesiredquiescent area enhanced.

In accordance with another feature of our invention we also provideanother form of settler which provides greater settling area. Referringto Figure 5 of the drawings there is shown a duplicate dissolver unit ofthat shown in'Figure l, the same numerals referring to like parts inboth gures. of Figure 1 is supplemented by an additional superimposedcone settling unit 26. It may be of similar design to the cone i6 andits settling area may have any desired relation in size to that of thelower cone i6. Herein, we have shown the conical units i6 and 26 asbeing equivalent in design and size. In the operation of this unit theliquor level is carried at or above the rim of the top settler 26 andwill be determined by the location of the outlet conduit 2l. The mixtureof solution and undissolved solute above the top of the inner shell 5,first sus the semer le, and then sus the semer is. Clear liquor is drawnoff simultaneously through outlets 2i and 2l. The rate of combinedwithdrawal will determine the duration of the retention period for anyparticular piece of equipment. The relative rates of withdrawal throughthe two outlets are preferably regulated so that the volumes withdrawnwill be in direct proportion to the settling capacities (i. e.capacities for In this Figure 5, the settler I6 producing clear liquor)of the units I6 and 26. With an apparatus similar to that describedherein, it will usually be desirable to control the withdrawal ofclarified liquor so that it is divided substantially equally between theconduits 21| and 2l. This control may be accomplished in any suitablemanner, as by valves or by using conduits of predetermined cross-sectionwhich will permit passage of only the desired ilow.

Undissolved solute which settles in the lower unit i6 is passed, asinFigure 1, into the circulating stream near the top of the well l. Soluteremoved from the upper cone 26 is preferably returnedto the circulatingstream in some manner which will not disturb the liquor in the lowercone. We accomplish this b'y providing a restricted section 28 from thebottom of the cone 26 to a point in the lower cone i6, but below theZone of quiescence within which clear liquor is produced. In this mannerwe produce clear liquor in each settler and return all the excess soluteto the circulating stream at-the top of the circulation well 5. Whenparticles settling in the upper cone are passed into the lower cone, theoutlet orifice i9 of the latter is made large enough to permit thecontinuous withdrawal of all the settled particles.

Movement of the excess or settled solute through the several settlerVorifices I9 and 33 is expedited by the usev of a helical screw 29similar to that described for Figure 1. By locating the helical screw 29around the impeller shaft 9 from a point belowthe lower settler to abovethe orifice of the upper settler, continued movement of solids-throughboth settlers is conveniently expedited. The use of such a screw sectionalso improves movement through the leg 28.

When using a multiple cone settler, as shown in Figure 5, the lowersettler is preferably arranged suilciently above the well 5 to provide aquiescent zone in which dissipation of the velocity head of the upwardmoving liquor takes place. Bailie plates 3B, as previously described,may be employed if desired to assist the dissipation of this velocityhead.

To assist in the maintenance of the quiescent Zone within the lowersettler I6 and to prevent turbulence therein as a result of settlingparticles in the liquor between the two settlers, we provide a skirt 3lwhich extends from the rim of the upper settler 26 to a level close tothe. rim of the lower settler. lower edge of the skirt 3l and the rim ofthe lower settler is made suiiicient to permit entrance of that volumeof liquor which it is desired to settle in the lower settler. Suitablevents as shown at 32 are provided near the juncture of the skirt withthe upper settler to permit the escape of air present between the uppersettler and the skirt when the apparatus is lled.

While we have described our invention by reference to the preparation ofsolutions having definite concentrations of dissolved constituents, itshould be obvious that it is also applicable in many instances where thedissolution of solids in a solvent is encountered. For example,lixiviation processes and leaching processes may be carried out in thepresent apparatus either where a particular concentration of solution isdesired or not. It is also obvious that in case of a leaching orlixiviation process provision may be made for withdrawal of solids. Theuse of our apparatus in multiple units with solids and liquors passingconcurrently may also be desirable in leaching The distance between thelor lixiviation processes. It is also apparent that the solute andsolventi may be separately introduced in the apparatus in place of beingintroduced through the common inlet 3a.

While the particular form of the apparatus here described is well'adapted to carry out the objects of this invention, it is to beunderstood that various modifications and changes may be made withoutdeparting from the principles thereof, and that this invention includesall such modications and changes as come within the scope oi theappended claims.

We claim:

1. An apparatus for dissolution or lixiviation, comprising means forforming a dissolving chamber for solute and'solvent having an inlet andan outlet, means for dividing the lower portion of said chamber intoconcentric portions of substantially equal cross-sectional area throughwhich solvent and solute may be circulated, a centrifugal impeller forcirculating solvent and solute therethrough, an inverted conical bailleplate providing a settling zone in the upper portion of said chamberinto which solution may overflow and having a discharge orifice for thereturn of settled particles to the lower portion of said chamber, andmeans for forcibly passing particles through said discharge orifice.

2. An apparatus for preparing solutions, cornprising means for forming achamber for holding solute and solvent, a circulating well dividing thelower portion of said chamber into up'and down circulation paths ofsubstantially equal cross-sectional area, a centrifugal impellerrotatably mounted insaid chamber to effect circulation of solute andsolvent through said path, means for forming a settling zone in theupper portion of said chamber into which solution and solute mayoverflow from said circulation path, means for withdrawing a clarifiedsolution from said settling zone, and means for returning solute fromsaid settling zone to said circulation paths.

3. An apparatus for dissolution or lixiviation, comprising means forforming a chamber for holding solute and solution, an invertedconicalshaped baie plate dividing said chamber into an upper settlingzone and a lower agitating Zone, said bale plate being disposed topermit influx of solution around its upper periphery and having a lowerdischarge orice, the agitating Zone of said chamber being provided withmeans for dividing the same into concentric up and down circulatin'gpaths, an impeller for circulating solvent and solute down the centralpath and up the annular return path, the shaft for said impeller beingprovided with means for forcibly ejecting settled particles through theorifice of said baiile plate.

4. An apparatus for dissolution or lixiviation, comprising means forminga chamber for holding a solute and solvent, a downwardly contractingbaie means in said chamber for dividing the same into an upper settlingzone and a lower zone for agitation of solvent and solute, said baiemeans permitting an influx of solute at its upper periphery and itslower end being opened for the return of settled particles to theagitating Zone, an inlet into the agitating zone, an outlet for solutionnear the upper central portion of the settling Zone formed by saidbaffle plate, a balile in said agitating zone dividing the same into upand down circulating paths, and means for forcing the solute and solventto pass through said circulating paths, the lower end of therst-mentioned baille being not substantially lower than the upper end ofsaid second-mentioned baille.

5. An apparatus for effecting dissolution or lixiviation, comprisingmeans for forming a dissolving chamber, a downwardly contracting baillein the upper portion of said chamber for forming a settling zone, abaille in the lower portion of the chamber for forming a circulatingagitating zone, the first-mentioned baille permitting an inilux ofsolute at its upper periphery at la point spaced substantially from thecirculating path of solute and solvent in the lower portion of saidchamber, said baille at its lower end being opened for return of settledparticles to the agitating zone, an inlet into the agitating zone, andan outlet for solution near the upper portion of the settling zoneformed by said first-mentioned baille.

6. An apparatus for eilecting dissolution or lixiviation, comprisingmeans for forming .a dissolving chamber, a downwardly contracting baillein the upper portion oi said chamber for forming a settling zone, abaille in the lower portion of the chamber for forming a circulatinglagitating zone, the first-mentioned baille permitting an iniluX ofsolute at its upper periphery at a point spaced substantially from thecirculating path of solute and solvent in the lower portion of saidchamber, said baille at its lower end being Opened for return of settledparticles to the agitating Zone, an inlet into the agitating zone, anoutlet for solution near the upper central portion of the settling zoneformed by said rst-mentioned baille, and an impeller for forcing soluteand solvent to circulate through said circulating path..

7. An apparatus for effecting dissolution of lixiviation, comprisingmeans for forming a dissolving chamber, a downwardly contracting baillein the upper portion of said chamber for forming a settling zone, abaille in the lower portion of the chamber for forming a circulatingagitating Zone, the ilrst-mentioned bale permitting an influx of soluteat its upper periphery at a point spaced substantially from thecirculating path of solutel and solvent in the lower portion of saidchamber, said baille at its lower end being opened for return of settledparticles to the agitating Zone, an inlet into the agitating zone, anoutlet for solution near the upper portion of the settling zone formedby said first-mentioned baille, and means for forcing settled particlesthrough the open end of said first-mentioned baille into the lowerportion of said chamber.

8. An .apparatus for eilecting dissolution or lixiviation comprisingmeans forming a dissolving WILLIAM H. ALLEN. ELIOT UNDERHILL. CHARLES F.RITCHIE.

